Method of and apparatus for grading magnetic sheet material



Oct. 17, 1939. J. J. BOWDEN 2,17s,7s4

METHOD OF AND APPARATUS FOR GRADING MAGNETIC SHEET MATERIAL Filed Sept. 22, 1936 3 Sheets-Sheet l ATTORNEY.

J. J. BOWDEN 2,176,784

ETIC SHEET MATERIAL METHOD OF AND APPARATUS FOR GRADING MAGN Filed Sept. 22, 1936 3 Sheets-Sheet 2 J? Goqcl A464 M MM ATTORNEY.

ATERIAL J. J. BOWDEN Oct. 17, 1939.

METHOD OF AND APPARATUS FOR GRADING MAGNETIC SHEET M INVENTOR.

ATTORNEY.

Patented a. 17, 1939 4 2,176,784

UNITED STATES PATENT OFFICE METHOD OF AND APPARATUS FOR GRAD- ING MAGNETIC SHEET MATERIAL James J. Bowden, Warren, Ohio Application September 22, 1936, Serial No. 102,991 4 Claims. (CL 209215) This invention relates to the grading of tin diagrammatic elevational view of one end porplate and has particular reference to rapid sepation, and Fig. l a similar view of the other end ration ofunderweight and overweight sheets portion, of an embodiment of my invention; from a series passing through the machine. Figs. 2 and 2" are fragmentary plan views of the In the production of tin plate for commercial end portions of the device shown respectively in 5 use the thickness of the sheets and consequently Figs. 1 and 1; Fig. 3 is a fragmentary plan view the total weight thereof must be up to a specified of the magnetic element or assembly; Fig. 4 is a requirement, otherwise the purchaser will reject wiring diagram showing one manner of conthe delivery. On the other hand, if the sheets trolling the magnetic means in response to the are overweight, the cost of metal to the manuposition of the sheets to be graded; Fig. 5 is a 10 facturer will be greater and his profit consediagrammatic, elevational view of afurther modquently reduced. It has been found in practice ified form and Fig. 6 is a fragmentary plan view that the output in the sheet mill industry necesthereof. sarily contains a certain percentage both of unefe g fi s to s- 1 t0 inclusive, the

derweight and overweight sheets and that as a numeral 42 indicates a conveyor of the endless 1 practical matter some system of grading these type trained over rollers or pulleys 43 and 44. for the removal of those falling outside the speci-- Suitable guide rollers 45 are provided for holdfied weight range is necessary. ing the upper stretch of the conveyor 42 in a The principal object of my invention is to proplane. Positioned above the conveyor 42 is a vide a magnetic device adapted to grade tin plate conveyor 46 trained over suitable guide rollers 20 and separate the underweight and overweight or pulleys 41 one or more of which may be driven sheets from the sheets of proper weight by means in any suitable manner as also may be those 43 of a construction which is simpler, more effective and 44. Within the conveyor 46 is a magnetic and less liable to get out of order than previous assembly indicated generally by the numeral 48 devices and to provide such a device capable of and consisting of a framework 49 carrying a 25 operating at a high speed as compared with preplurality, and preferably a large number, of magvious devices. nets 50. The magnets 50 are preferably electro- A further object of the invention is to promagnets but permanent magnets can be used. vide a device for grading sheets of magnetic ma- The magnets 50, if electromagnets, may be terial in which the force of magnetic attraction wound so as to present alternate rows of north 30 is adjusted to discriminate between sheets acand south poles toward the conveyor or all north cording to their weight and in which means are poles may be presented in the same direction. provided for determining the path of movement The former arrangement provides a magnetic of a sheet of material according to the efiect of circuit of lower reluctance; the latter a slightly the magnet on the same, that is to provide for greater uniformity of distribution of the whole 35 conveying the sheet in one path if its weight is field. The framework 49 is provided with such that the magnet lifts it or retains it susthreaded studs 5! received in slots 52 in supportpended and in a different path if its weight is ing elements 53 whereby the magnetic assembly such that the magnet does not lift it or retain may be vertically adjusted. The magnetic as- 43 it suspended. sembly is preferably as large as or larger in A further object is to provide forapplication horizontal area than that of any of the sheets of a critical magnetic attraction on a sheet at a which it may be desired tograde, it being undertime when such sheet has reached a predeterstood that it will be effective to grade the sheets mined position in respect to the magnetic means, of any smaller size. When sheets come beneath that is, at a time subsequent to its initial enthe magnetic assembly 48, if they are of suflid5 trance into the sphere of magnetic influence. ciently light weight, they will be attracted to A further object is to provide for exerting on and held against the lower stretch of the conveythe sheet a force proportional to the area of or 46 until they can be delivered to the consuch sheet and to do so substantially indepenveyor 54 which will deliver them to a chute 55.

5c dently of the total area whereby sheets of difier- It is to be noted that in this case there is no cut sizes may be graded without the necessity abrupt change in direction in the progress of of adjusting the machine. the sheet.

Other objects will be in part apparent and in It is contemplated that this device will be run part pointed out hereinafter in connection with at a speed sufiiciently great that the inertia of 55 the accompanying drawings wherein Fig. l. is a the sheets being graded will be considerable, g5

. will also prevent any danger of the sheets dropping back into contact with the conveyor 42. In this case, it is contemplated that the magnets 50 will be quite strong and placed at a substantial distance from the conveyor. This minimizes the effect of Warpage of the sheets and vibration of the machine or its supports. In view of the relation of the attracting force to the distance from the magnets, (inversely proportional to the square of the distance) the percentage variation in distance due to warpage or vibration may be relatively great without making much difi'erence in the weight of sheet which can be lifted. For example, suppose the magnets are one inch from the conveyor and, due to warpage or vibration, the sheet is an average distance of one sixtyfourth of an inch closer to the magnet than it theoretically should be, then the attracting force exerted on the sheet will be only about three percent greater than if the sheet were perfectly flat. One sixty-fourth of an inch average warpage would allow for a maximum of one thirty-second of an inch at high spots. Any regular warpage, such as slight curvature due to the stock having been fed from a roll, can be compensated for by the setting of the machine; and, likewise, usually occurring irregular warpage. Sheets having an irregular warpage of, e. g., one-eighth of an inch would require positioning of the magnets at a distance of-about eight inches for the same accuracy.

Supported to the right along the conveyor 42 is a similar conveyor 56 provided with a similar magnetic assembly, which, on account of its identity with that shown in connection with conveyor 46, is given the same reference numerals. The operation of the assembly associatedwith the conveyor 56 is identical with that previously described and operatedin the same manner except that it is placed somewhat closer to the conveyor 42 whereby to lift sheets of greater weight. It may be. positioned at the same distance and provided with magnets of somewhat greater stengthor magnets of the same inherent strength may be energized more strongly. Sheets attracted to the conveyor 56 will be delivered in the same manner to the conveyor 51 from which they will be delivered to the chute 58. Sheets of too great weight to be attracted by either of the magnetic means will be delivered from the conveyor 42 to the chute 59.

While the device of Figs. 1, 1 may be operated with either electromagnets or permanent magnets continuously energized, the operation is somewhat more satisfactory if the magnets are intermittently varied in strength in response to the positioning of a sheet therebeneath. One means of effecting this result is to provide for weakening the currentsupply to the magnets 50 when a sheet is partially thereunder and increasing the current to the magnet responsive to the positioning of a sheet under orsubstantially under the magnetic means.

In Figs. 1, 1 and 4 I have shown a source of light 60 and a light operated switch 6| positioned adjacent the rear edge of the magnetic means whereby, when the sheet is moved to a position beyond the'light, light from the. source 60 will fall upon the light responsive switch 6| and cause a circuit to beclosed whereby the magnets will be energized to full strength' In order that a sheet which may have been previously attracted to the upper conveyor may not fall back to the lower conveyor, I provide a resistance 62 in parallel with the switch 6| so that the magnets will at all times be energized sufllciently to support a sheet which has been elevated. The resistance 62 will be of such value that the sheet will not be permitted to drop and such resistance will be shunted out by the switch 6|.

It is to be understood that in the operation of this device the rate of feed will be such that the successive sheets of material to be graded will be spaced a little apart from each other, sufiiciently to allow the light passing between them to fall upon the light responsive switch 6|. It is to beunderstood that the conveyor which carries the sheets will have to be provided with a transparent or translucent zone passing between the light 60 and the switch 6|, or the equivalent means such as a split belt or perforations as indicated at 63 will have to be employed.

Referring now to Figs. and 6, wherein is illustrated a further modified form of the invention, it will be seen that I have provided a conveyor I0, trained over pulleys H and 12', which may receive the sheets 13 to be graded from any suitable source and convey them beneath a conveyor belt 14 trained over pulleys l5 and 16. It is contemplated that the upper stretch of the conveyor I0 will be spaced below the lower stretch of that of 14 just slightly more than the thickness of the sheets 13. Supported immediately above the lower stretch of the conveyor 14, I provide a series of banks of magnets, three such banks being shown. These banks may be supported by longitudinally extending strips 11 which I have shown as supporting'the pulleys 15 and 16. The banks of magnets 18, 19 and 80 are attached, adjustably if desired, to the strips I1 and are separated from each other by magnetic shields 8| and 82 which may be composed of soft iron of sufiicient thickness to substantially isolate the banks of magnets from each other. The con veyors and 14 are composed of non-magnetic material so as not to influence the magnetic effect of the banks on the sheets.

The first bank 18 is to be of such magnetic strength that it will readily elevate any and all of the sheets to be graded. The second'bank of magnets 19 is to be of such strength that those sheets 13 which are heavier than a predetermined weight will drop oif and slide down the chute 83, all sheets lower than such predetermined weight being carried on into the influence ofthe next bank of magnets 80. The bank 80 is to be of such strength that the sheets 13' of intermediate grade, that is, within theallowable tolerances for a particular requirement, will be discharged and slide down the chute 84. Sheets 13 which are too light, that is, below a predetermined weight, will be carried out of the influence of the bank 80 and slide down the shute 85. The individual magnets of the various banks may be carried by a block or plate 86 suitably attached to the strips 11.

It is contemplated that the lower stretch of the conveyor 14 may slide against the lower surfaces This application is a continuation in part 01 E my copending application Serial No. 79,325, filed May 12, 1936.

While I have shown and described two embodiments of my invention, I wish it to be understood that the same may be realized by the use of different structures and that I am limited only in accordance with the appended claims and the v prior art.

' Having thus described my invention, what I claim is:

1. The process of grading according to weight sheets of material of substantially uniform magnetic susceptibility comprising subjecting such sheets first to a magnetic field capable of lifting the same, and then conveying the sheets thus lifted within the influence of a magnetic field of such strength as to release such of said sheets as are above a predetermined weight.

2. The process of; grading according to weight sheets of material of substantially uniform magnetic susceptibility comprising conveying a series of such sheets one at a time within the influence of a magnetic field capable of lifting any and all of such sheets, and thereafter conveying the sheets thus lifted, one at a time, within the influence of a plurality of magnetic fields of lower and critical strength thereby to release such sheets at different points according to their predetermined weights and the strength of the magnetic fields which release them.

3. The process of grading according to weight sheets of material of substantially uniform magnetic susceptibility comprising conveying a series of such sheets one at a time within the influence of a. magnetic field capable of lifting any and all of such sheets,v and thereafter conveying the sheets thus lifted within the influence of a plurality of magnetic fields of lower and critical strength such as to release such sheets according to predetermined weights and the strength of the magnetic fields which release them, such magnetic fields being sufficiently diffuse to act with approximate uniformity over the entire area of such sheets.

4. A magnetic separator for grading magnetic sheet material, comprising,'in combination, a conveyor for sheets to be graded, magnetic sheet deflecting means extending along said conveyor and being of an extent to subject the major portion of the area of a sheet to its magnetic influence and being of a strength to deflect sheets of less than predetermined mass, and conveyor means for conveying deflected sheets away from said first conveyor, said magnetic deflecting means including means for normally producing a magnetic field of suflicient intensity to hold a deflected sheet against return to said first conveyor, and means responsive to the positioning of a sheet substantially entirely within the magnetic field for increasing the intensity of such magnetic field to a predetermined maximum value.

JAMES J. BOWDEN. 

